Turbochargers can include various types of bearings to support a shaft and wheel assembly (SWA). As an example, a turbocharger may include a rolling element bearing that includes an inner race fit to a shaft where the inner race is rotatably supported by rolling elements set within an outer race. In such an example, a mechanism may be provided to avoid or limit rotation of the outer race while optionally allowing for lubricant film formation between the outer race and a bore of a turbocharger bearing housing (e.g., a center housing disposed between a turbine housing and a compressor housing).
As another example, a turbocharger may include a journal bearing with inner journal surfaces to support a shaft via formation of a lubricant film between the shaft and the inner journal surfaces. In such an example, a mechanism may be provided to avoid or limit rotation of the journal bearing while optionally allowing for lubricant film formation between the journal bearing and a bore of a turbocharger housing (e.g., a center housing disposed between a turbine housing and a compressor housing). Thus, in comparison to a rolling element bearing, a journal bearing may include inner and outer lubricant films.
A journal bearing may be set within a bore of a housing as a fully-floating or semi-floating journal bearing. A fully-floating journal bearing can rotate within the bore a full 360 degrees, for example, parasitically responsive to rotation of a shaft supported by the journal bearing. A semi-floating journal bearing is located azimuthally to avoid or limit rotation. For example, a semi-floating journal bearing may include an aperture configured for receipt of a locating pin where a clearance between a perimeter of the aperture and a perimeter of the locating pin limits rotation of the semi-floating journal bearing with respect to a bore of a housing. A locating pin may also axially locate a semi-floating journal bearing within a bore of a housing. However, a locating pin and aperture arrangement can allow for some amount of radial movement of the semi-floating journal bearing within a bore to provide for radial “floating”. Radial floating allows a lubricant film or lubricant films disposed between an outer surface or outer surfaces of a journal bearing and an inner surface or inner surfaces of a housing (e.g., that define a bore) to absorb or damp energy. For example, such a lubricant film or films may damp vibrational energy.
Where a locating pin is employed to axially and azimuthally locate a journal bearing in a bore of a housing, the locating pin may be aligned with gravity such that the journal bearing and shaft and wheel assembly can settle to a bottom side of the bore. For a turbocharger lubricated by oil of an internal combustion engine, when the engine is started, pressurized oil can enter a bore and fill clearances between the bore and a journal bearing to thereby form lubricant films. Radially movement of a journal bearing within a bore in a direction aligned with gravity can help minimize friction and wear of a perimeter of an aperture in a journal bearing and a perimeter of a locating pin disposed at least partially therein.
As to axially locating a journal bearing via a locating pin disposed in an aperture of the journal bearing, a perimeter of the aperture and a perimeter of the locating pin are likely to experience axial thrust forces during turbocharger operation. Axial thrust forces may be directed in a direction from a turbine wheel to a compressor wheel or vice versa. A shaft and turbine wheel assembly supported by a journal bearing may include an axial face that abuts a turbine end of the journal bearing. For axial thrust forces in a direction from the turbine wheel to a compressor wheel, the axial face of the shaft and turbine wheel assembly may impact the journal bearing. In turn, such force can be transmitted to a locating pin disposed in an aperture of the journal bearing. Over time, the force may cause a perimeter of the aperture or a perimeter of the locating pin to wear, which may alter a clearance or clearances between the locating pin and the journal bearing. Wear may also occur between a locating pin and a socket in a housing that receives the locating pin. For example, a locating pin and socket may include matching threads that allow the locating pin to be screwed into the housing. Axial thrust forces and possibly other forces applied by a journal bearing to such a locating pin may cause the locating pin to become loose or displaced. Misalignment of the locating pin stemming from such wear can detrimentally impact performance of one or more lubricant films of a semi-floating journal bearing.
Referring again to thrust forces, as to rolling element bearings, such forces may be transferred from a shaft to an inner race to rolling elements and to an outer race. As a journal bearing does not retain a shaft in such a manner, a journal bearing can include so-called thrust pads on a compressor end, a turbine end or both. A thrust pad may be a feature that allows lubricant to flow, collect, etc., to minimize impact caused by another component being axially thrust toward an end of a journal bearing. Further, as to an axial face formed as by a shoulder between a shaft and a hub end of a turbine wheel, such a face may impact a turbine end of a semi-floating journal bearing with both axial and rotational forces. As to a rolling element bearing, again, as a shaft is fixed to an inner race of rolling elements disposed within an outer race, an axial face of a shaft and turbine wheel assembly is unlikely to impact an end of the rolling element bearing. For example, clearance between an axial face of a shaft and turbine wheel assembly may be fixed upon fixing the shaft to an inner race within a rolling element bearing.
Various technologies and techniques described herein are directed to journal bearings, housings, assemblies, etc., which may improve turbocharger performance, longevity, etc.